This invention relates to a rubber composition, and more particularly to a rubber composition comprising a fluoroelastomer and an ethylene-.alpha.-olefin copolymer rubber excellent in processability such as processability on roll and/or in extruder, heat resistance, steam resistance, weather resistance, compression set and resistance to compressive load.
The requirement for performance of rubber material has recently become severe year by year, and a change has started in the type of rubber material to be used, fluoroelastomer excels other special rubbers in solvent resistance, heat resistnace, chemical resistance and weather resistance, and the demand thereof is increasing in fields of industrial product, automobile and aircraft year by year. However, the fluoroelastomer is much more expensive than the other elastomers, and has higher specific gravity than the others. Therefore, the price of products made therefrom becomes remarkably high, and hence, the field in which fluoroelastomer is used has been limited. It has become difficult for one sort of rubber stock to meet simultaneously the inconsistent requirements of high performance and low price as mentioned above.
In order to meet such requirements, it has been proposed to mix a fluoroelastomer with another elastomer. The elastomer to be mixed with the fluoroelastomer is often an elastomer having a polar group such as an acrylonitrile-butadiene rubber, an acrylic rubber, a chlorohydrin rubber or the like.
Even when such an elastomer having a polar group is mixed with the fluoroelastomer; however, as satisfactory performance has been obtained because it has been difficult to obtain a uniform mixing state between the elastomer and the fluoroelastomer.
On the other hand, Japanese Patent Application Kokai No. 34,935/87 proposes a method of mixing a fluoroelastomer with an ethylene-.alpha.-olefin copolymer rubber which is a non-polar elastomer, in which the ethylene-.alpha.-olefin copolymer rubber is first partially crosslinked and then mixed with the fluoroelastomer. Said partial crosslinking is achieved by dissolving the ethylene-.alpha.-olefin copolymer rubber in a solvent such as n-hexane or the like, re-emulsifing the resulting solution and then partially crosslinking the copolymer rubber in the form of a latex with an organic peroxide. This method is, however, complicated in steps because it requires the steps of dissolution of rubber, re-emulsification, removal of solvent and partial crosslinking in the latex state, and the method is also disadvantageous in energy. In addition, the composition obtained tends to be inferior in compression set.